Complexity of life 3.5 billion years ago?

[Lluis Ribas]

      Hi,

    I would like to hear educated opinions on the following question :

    What may have been the complexity of life on earth at the moment of
   
    appearance of the eukaryota/archibacteria superkingdoms ?.

    Basicly should we assume that a large number of distinc unicellular 
   
    (supposedly) organisms existed ?. that would imply that we should be able 
  
    to link eukaryote/archibacteria evolution to a subpopulation of the

    eubacteria.

    Or was the overall complexity rather small so that most of today's 
  
    eubacteria originated from a reduced number of organisms that had not 
  
    evolved much when the eukarya/archaea branched out ?.

    References on the subject would also be highly appreciatted .


                  Thank you,  Lluis